Cooling system for high performance solar concentrators

ABSTRACT

Techniques for cooling concentrating solar collector systems are provided. In one aspect, an apparatus for cooling a photovoltaic cell includes a heat exchanger having a metal plate with a bend therein that positions a first surface of the metal plate at an angle of from about 100 degrees to about 150 degrees relative to a second surface of the metal plate, and a plurality of fins attached to a side of the metal plate opposite the first surface and the second surface; a vapor chamber extending along the first surface and the second surface of the metal plate, crossing the bend; and a cladding material between the vapor chamber and the heat exchanger, wherein the cladding material is configured to thermally couple the vapor chamber to the heat exchanger. A photovoltaic system and method for operating a photovoltaic system are also provided.

FIELD OF THE INVENTION

The present invention relates to concentrating solar collectors and moreparticularly, to techniques for cooling concentrating solar collectorsystems.

BACKGROUND OF THE INVENTION

Concentrating solar collectors operating at extreme concentrations (fromabout 500 suns to about 2,000 suns) require optimal cooling systems todissipate heat that evolves in the photovoltaic cell from incident solarradiation. A variety of cooling methods are available including liquidcooling, forced air and convective cooling. Of these methods, convectivecooling is often viewed as the most desirable for cost and reliabilityreasons.

A common strategy to implement high performance collection is toconstruct an array of concentrating solar collectors (Fresnel lenses forexample). In such an array, each lens is associated with a givenphotovoltaic cell. In conventional designs, these photovoltaic cellsmust be individually packaged, structurally supported and cooled. Theseelements are structurally connected and move as a single unit to trackthe sun on a single two axis drive system. It is normal practice toelectrically connect individual photovoltaic cells in series to enablesystem operation at higher voltage. In systems comprising manyphotovoltaic cells, this voltage is large and electrical isolation ofcomponents is necessary for safety and reliability.

Concentrating solar collector systems track the sun in order to maintainoptical focus of the concentrated sunlight on the photovoltaic cells. Intypical designs, the tracking must be accurate to angles of a degree orless relative to the sun. Tracking may be performed by rotating theassembly in the azimuth and then the elevation to follow the sun.

A cooling system affixed to a photovoltaic cell on a concentrating solarcollector will therefore experience angular rotations ranging as much asfrom zero degrees to 90 degrees in elevation over the course of thesolar day depending on the day of the year and geographic location. Itis desirable that the cooling system operate optimally over this rangeof angles.

Therefore, techniques for cooling concentrating solar collector systemsthat perform optimally at different elevation angles and provideelectrical isolation to the photovoltaic cells in the system would bedesirable.

SUMMARY OF THE INVENTION

The present invention provides techniques for cooling concentratingsolar collector systems. In one aspect of the invention, an apparatusfor cooling a photovoltaic cell is provided. The apparatus includes aheat exchanger comprising a metal plate with a bend therein thatpositions a first surface of the metal plate at an angle of from about100 degrees to about 150 degrees relative to a second surface of themetal plate, and a plurality of fins attached to a side of the metalplate opposite the first surface and the second surface; a vapor chamberextending along the first surface and the second surface of the metalplate, crossing the bend, such that during operation when thephotovoltaic cell is attached to either the first surface or the secondsurface of the metal plate the vapor chamber is positioned to transportheat away from the photovoltaic cell; and a cladding material betweenthe vapor chamber and the heat exchanger, wherein the cladding materialis configured to thermally couple the vapor chamber to the heatexchanger.

In another aspect of the invention, a photovoltaic system is provided.The photovoltaic system includes a cooling apparatus having a heatexchanger having a metal plate with a bend therein that positions afirst surface of the metal plate at an angle of from about 100 degreesto about 150 degrees relative to a second surface of the metal plate,and a plurality of fins attached to a side of the metal plate oppositethe first surface and the second surface; a vapor chamber extendingalong the first surface and the second surface of the metal plate,crossing the bend; a cladding material between the vapor chamber and theheat exchanger, wherein the cladding material is configured to thermallycouple the vapor chamber to the heat exchanger. The photovoltaic systemfurther includes at least one photovoltaic cell thermally coupled to thevapor chamber; and a concentrating solar collector attached to eitherthe first surface or the second surface of the metal plate andsurrounding the photovoltaic cell.

In yet another aspect of the invention, a method for operating aphotovoltaic system is provided. The method includes the followingsteps. A photovoltaic system is provided. The photovoltaic systemincludes a cooling apparatus. The cooling apparatus includes a heatexchanger having a metal plate with a bend therein that positions afirst surface of the metal plate at an angle of from about 100 degreesto about 150 degrees relative to a second surface of the metal plate,and a plurality of fins attached to a side of the metal plate oppositethe first surface and the second surface, a vapor chamber extendingalong the first surface and the second surface of the metal plate,crossing the bend, and a cladding material between the vapor chamber andthe heat exchanger, wherein the cladding material is configured tothermally couple the vapor chamber to the heat exchanger. Thephotovoltaic system also includes at least one photovoltaic cellthermally coupled to the vapor chamber and a concentrating solarcollector attached to either the first surface or the second surface ofthe metal plate and surrounding the photovoltaic cell. The photovoltaicsystem is rotated to place the photovoltaic cell at a plurality ofpositions relative to a light source.

A more complete understanding of the present invention, as well asfurther features and advantages of the present invention, will beobtained by reference to the following detailed description anddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a concentrating solar collector with ahigh power cooling system attached thereto according to an embodiment ofthe present invention;

FIG. 2 is a diagram illustrating one exemplary configuration of thecooling system of FIG. 1 according to an embodiment of the presentinvention;

FIG. 3 is a diagram illustrating an enlarged view of a portion of thecooling system of FIG. 2 according to an embodiment of the presentinvention;

FIG. 4A is a diagram illustrating one exemplary positioning of thecooling system of FIG. 1 and how at least one portion of the coolingapparatus is in a substantially vertical orientation according to anembodiment of the present invention;

FIG. 4B is a diagram illustrating another exemplary positioning of thecooling system of FIG. 1 and how at least one portion of the coolingapparatus is in a substantially vertical orientation according to anembodiment of the present invention;

4C is a diagram illustrating yet another exemplary positioning of thecooling system of FIG. 1 and how at least one portion of the coolingapparatus is in a substantially vertical orientation according to anembodiment of the present invention;

FIG. 5A graphically depicts the positioning of the cooling apparatus inFIG. 4A and illustrates how a first portion of the cooling apparatus isin a vertical position according to an embodiment of the presentinvention;

FIG. 5B graphically depicts the positioning of the cooling apparatus inFIG. 4B and illustrates how both a first portion and a second portion ofthe cooling apparatus are in a vertical position according to anembodiment of the present invention;

FIG. 5C graphically depicts the positioning of the cooling apparatus inFIG. 4C and illustrates how a second portion of the cooling apparatus isin a vertical position according to an embodiment of the presentinvention;

FIG. 6 is a diagram illustrating an exemplary two-axis drive systembeing used in conjunction with the present photovoltaic system accordingto an embodiment of the present invention; and

FIG. 7 is a diagram illustrating an enlarged view of a portion of thepresent plate fin heat exchanger that highlights a plate and finsattached thereto as well as an optional wrapper that caps the fins toconstrain air flow along the fin assembly according to an embodiment ofthe present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Provided herein are techniques for cooling high performanceconcentrating solar collectors in photovoltaic systems that operateoptimally at different elevation angles and provide electrical isolationto the photovoltaic cells in the system. FIG. 1, for example, is adiagram illustrating a photovoltaic system that includes a concentratingsolar collector with a high power cooling apparatus 103 attachedthereto. Cooling apparatus 103 is capable of operation at high solarconcentrations (i.e., at greater than 50 Watts per square centimeter(W/cm²)). The concentrating solar collector includes a collector optic101 (i.e., a lens) and an enclosure support 102. The concentrating solarcollector is attached to the high power cooling apparatus 103 using,e.g., mechanical means such as fasteners (e.g., screws) or by way of anadhesive.

The concentrating solar collector may be used individually (as shown inFIG. 1) or in an array, and may be attached to a two-axis drive system.A two-axis drive system (azimuth and elevation) would allow thephotovoltaic system to be pointed in two dimensions to follow the sun.Telescopes employ similar two-axis drive systems to track stars. Anexample of a two-axis drive system suitable for use with the presentphotovoltaic system is shown in FIG. 5, described below.

As will be described in detail below, cooling apparatus 103 (to which aphotovoltaic cell is attached) includes a bent fin convective heatexchanger coupled to an electrically isolated heat pipe (or vaporchamber) that is directly coupled to the photovoltaic cell using a metalthermal interface. An exemplary configuration of cooling apparatus 103is depicted in detail in FIG. 2, described below.

During operation of the photovoltaic system, light energy (from the sun)is focused on the photovoltaic cell by the concentrating solarcollector. The photovoltaic cell will convert (a portion) of the lightenergy into electricity. However, the photovoltaic cell is in most casesnot 100% efficient. Therefore, an un-used portion of the light energyhas to be carried away from the photovoltaic cell (in the form of heat).Thus, the light energy from the sun is a source of heat (heat source) tothe photovoltaic system. By way of the cooling apparatus 103, this heatis carried away from the photovoltaic cell. See description below.

FIG. 2 is a diagram illustrating one exemplary configuration of coolingapparatus 103 (of FIG. 1). In this example, cooling apparatus 103includes a bent fin naturally convective heat exchanger 201 thermallycoupled to an electrical insulation-clad vapor chamber 204 (in theexample shown in FIG. 2, and elsewhere herein, the vapor chamber 204 isa heat pipe, however any other type of vapor chamber configuration maybe employed in the same manner) (that is electrically, but not thermallyisolated, from the heat exchanger by the electrical insulation) which inturn is thermally coupled to a thermal spreader plate 203 (eitherdirectly or through a thermal interface material (suitable thermalinterface materials are provided below)) and photovoltaic cell 202. Theuse of a thermal spreader plate is optional, as photovoltaic cell 202may alternatively be directly attached to the vapor chamber 204 (by wayof a thermal interface material, see below) or to an intermediatesubstrate (also by way of a thermal interface material). It is furthernoted that the photovoltaic cell 202 may be thermally coupled to theheat pipe through a conductive substrate that comprises a conductivepattern layer on a thermally conductive substrate with appropriatethermal interfacing. This allows direct and convenient electricalconnection to the cell.

As described above, the cooling apparatus serves to remove heat from thephotovoltaic cell. As explained above, the heat source (duringoperation) is the light energy from the sun incident on the photovoltaicdevice, a portion of which needs to be carried away from thephotovoltaic cell as heat. The heat flow through the exemplaryconfiguration shown in FIG. 2 is now described. The heat from thephotovoltaic cell enters the vapor chamber 204. A heat pipe is anextremely efficient heat spreader. The bent fin heat exchanger 201(thermally coupled to the vapor chamber 204) then convects the heat fromthe vapor chamber 204 into the air. The vapor chamber 204 permits theheat to be spread over the whole bent fin heat exchanger 201, thusallowing for more effective cooling by apparatus 103.

As provided above, the bent fin heat exchanger 201 is a naturallyconvective heat exchanger. A naturally convective heat exchanger relieson the buoyancy change of air to convect heat into the air (which occursas a result of placing a hot object in air). By way of example only,natural convection is how baseboard heaters heat a dwelling.

Photovoltaic cell 202 can be a triple-junction solar photovoltaicconverter cell for high efficiency or a single semiconductorphotovoltaic cell (e.g., a silicon solar cell optimized for high lightconcentration). This optimization includes but is not limited to dopingand enlarging the grid, as is known in the art, for improved seriesresistance given the higher current resulting from light concentration.Triple junction solar converter cells and single semiconductorphotovoltaic cells are known to those of skill in the art and thus arenot described further herein.

According to an exemplary embodiment, heat exchanger 201 is a plate finheat exchanger, made of a suitable metal (such as, copper, brass, steeland/or aluminum), wherein the fins are attached to one side of theplate, as shown in FIG. 2. As also shown in FIG. 2, the plate fin heatexchanger 201 has a bend therein that positions one surface thereof(i.e., a first surface) at an angle θ relative to another surfacethereof (i.e., a second surface). In one exemplary configuration, thebend positions the first surface of the plate fin heat exchanger at anincluded angle θ of from about 100 degrees to about 150 degrees, e.g.,at an angle of about 140 degrees, relative to the second surface of theplate fin heat exchanger. In most embodiments this bend is not large. Aback view of the heat exchanger is also provided in FIG. 2 to illustratethat, according to an exemplary embodiment, the fins are attached to aback of the plate.

As shown in FIG. 2, the vapor chamber 204 extends along the first andsecond surfaces of the plate fin heat exchanger crossing the bendtherein. As will be described in detail below, this particularconfiguration permits, during operation, at least one of the surfaces ofthe plate fin heat exchanger (and consequently a portion(s) of the vaporchamber) to always be in a substantially vertical orientation when theheat exchanger is rotated to place the photovoltaic cell at a goodposition to capture light from a light source (i.e., the sun). Air tendsto rise up in a vertical direction. Thus, since the plate fin heatexchanger is a naturally convective heat exchanger (see above), then itis beneficial for at least a portion of the plate fin heat exchanger tobe in a substantially vertical orientation during operation to enhanceconvection of heat from the plate fin heat exchanger to the air. Ofcourse, the plate fin heat exchanger will operate (naturally convectheat to the air) even if the plate fin heat exchanger is not in asubstantially vertical orientation. However, the efficiency at which itoperates will be diminished.

The embodiments configured as shown in FIG. 2 particularly benefit fromthe azimuth elevation tracking (see FIG. 6, described below) in that thefins are always in a plane that includes the surface normal to theearth. The elevation angle is shown in FIG. 6. It is noted that theembodiment is still practical in alternate drive strategies such aselevation azimuth. Though elevation azimuth is not optimal, as long as avertical flow component is possible, improved cooling will result.Additionally, the fins may be optionally covered with a metal or plasticwrapper that forms a convective airflow channel containing the fins. SeeFIG. 7, described below. Alternately, the fins may be slotted to allowsome cross flow of air.

Photovoltaic cells used for solar concentrators are typicallyconstrained to operation at or below from about 85 degrees Celsius (°C.) to about 110° C. for both efficiency and lifetime considerations(lifetime expectations for solar systems are on the order of 20 to 30years). Operation is desired in a range of climates, including desertclimates where ambient temperatures up to 45° C. can occur. Therefore,in the case of a desert climate the thermal budget for a cooling systemis 40° C. At an incident power of 200 W/cm² and an operating power of 60watts (W), the overall cooling system performance requirement is 0.30°C./W. This performance requirement constrains the elements of thecooling system to the high performance category (such as those describedherein which are capable of operation at high solar concentrations,i.e., at greater than 50 W/cm²). For less concentrated systems, forexample, in the 500 sun range, system performance in the 1.2° C./W isacceptable.

Vapor chambers, such as heat pipes (a heat pipe is a kind of vaporchamber), and the functioning thereof are known to those of skill in theart. In general however vapor chambers cool by way of an enclosedworking fluid (e.g., water) that serves to carry heat away from a heatsource by vaporization. The fluid recondenses in other cooler areas ofthe vapor chamber. A wick delivers the fluid back to the location of theheat source. While the substantially cylindrical shape of a heat pipemakes it convenient for the present techniques, if desired either a heatpipe or a vapor chamber may be used interchangeably in any of theembodiments presented herein.

Advantageously, this configuration enables the use of a thermalinterface material, such as solder, a liquid metal thermal interface ora conductive particle filled organic paste or gel (not visible in thisdepiction), that directly thermally connects the photovoltaic cell tothe spreader plate, the heat pipe/vapor chamber or an intermediatesubstrate while providing electrical isolation (by way of the electricalinsulation around the heat pipe) to the photovoltaic element. That way,maximum heat transfer from the photovoltaic cell to the cooling systemcan occur. Further, given the shape of bent fin naturally convectiveheat exchanger 201, maximum cooling performance can be attained at arange of operating angles. An enlarged view of portion 206 of coolingapparatus 103 is shown in FIG. 3.

FIG. 3 is a diagram illustrating an enlarged view of portion 206 (ofFIG. 2). As shown in FIG. 3, and as described above, photovoltaic cell202 is thermally coupled to thermal spreader plate 203. Thermal spreaderplate 203 is thermally coupled to vapor chamber 204. In this particular,preferred embodiment, vapor chamber 204 is clad in a thermallyconductive but electrically insulating cladding material 304. Thecladding material 304 thermally connects the vapor chamber 204 to theheat sink 201. Cladding material 304 can be made of a plastic, a ceramicand/or a glass material. As highlighted above, this configurationenables the use of a thermal interface material, such as a solder, aliquid metal thermal interface (such as a liquid metal alloy), thermalgrease, a conductive particle filled organic thermal paste or gel (e.g.,a particle impregnated polymer) and/or a phase change material thatdirectly connects the photovoltaic cell to the thermal spreader platewhile providing electrical isolation to the photovoltaic cell.

As highlighted above, the use of a thermal spreader plate is optionaland embodiments are presented herein (not shown) where the photovoltaiccell is directly thermally attached to the heat pipe (by way of athermal interface material). By way of example only, the photovoltaiccell can be soldered directly to the heat pipe. Alternatively, thephotovoltaic cell can be attached to an intermediate substrate (notshown) which is in turn thermally attached to thermal spreader plate 203(again by way of a thermal interface material). The intermediatesubstrate can include a metalized intermediate substrate of electricallyinsulating but thermally conductive material, such as aluminum nitrideor aluminum oxide which is bonded to the thermal spreader plate surface.In yet another variation, the photovoltaic cell can be attached to anintermediate substrate (not shown) which is in turn directly thermallyattached to the heat pipe (again by way of a thermal interfacematerial).

Introducing intermediate elements between the photovoltaic cell and theheat pipe, such as a thermal spreader plate and/or an intermediatesubstrate allows the engineer to introduce electrical isolation,mechanical strain relief, part handling capability, mechanical stabilityand thermal expansion matching. However, these elements are introducedat a thermal cost and must be factored into the desired systemperformance to select the optimal embodiment for a given concentratorsystem.

In one embodiment, the vapor chamber comprises all or part of themechanical structural support of the photovoltaic cell. For example, ifthe photovoltaic cell is attached directly to the vapor chamber using asolder thermal interface, the assembly becomes a solid unit that can beadded or removed from the system as a module and affixed using screwsbetween the module and the heat sink. The system has been illustratedherein as a single lens concentrating light on a single cell and heatsink for simplicity. It is noted however that the bent fin may bepracticed for arrays of lenses and cells.

It is notable that a naturally convective heat exchanger such as bentfin naturally convective heat exchanger 201 (of FIG. 2) operatesoptimally in an orientation that allows rising convective air currentsto move parallel to cooling fin surfaces. Heat pipes and vapor chambersoperate optimally in a substantially vertical orientation with the heatproducing element (in this case the photovoltaic cell) located at thelowest point of the heat pipe/vapor chamber. This orientation allowsgravity to assist the return of the working fluid to the heat source inthe vapor chamber. Heat pipes and vapor chambers will also operate wellin a horizontal orientation. However, in cases where the heat source islocated above the heat sink region of the vapor chamber or heat pipe itis common to see degraded performance.

FIGS. 4A-C are diagrams illustrating how cooling apparatus 103 in avariety of different orientations experiences predominately verticalairflow during operation. Namely, FIGS. 4A-C show cooling apparatus 103in three elevation angles and how in all three cases at least oneportion of the heat exchanger 201 (due to its bent shape) is in apredominantly vertical orientation. As described above, air tends torise up in a vertical direction. Thus, since the plate fin heatexchanger is a naturally convective heat exchanger (see above), then itis beneficial for at least a portion of the plate fin heat exchanger tobe in a substantially vertical orientation during operation to enhanceconvection of heat from the plate fin heat exchanger to the air.

As is apparent from FIGS. 4A-C, cooling apparatus 103 pivots along anaxis 402 (pointing into/out of the page) which permits positioning theconcentrating solar collector relative to the changing position of thesun, i.e., horizontal (FIG. 4A), intermediate (FIG. 4B) and vertical(FIG. 4C) positions relative to solar positions A, B and C,respectively.

Namely, in FIG. 4A, the concentrating solar collector attached tocooling apparatus 103 is shown in a horizontal elevation and asignificant portion of the heat exchanger 201 is in a predominantlyvertical convective air flow. In FIG. 4B, the concentrating solarcollector attached to cooling apparatus 103 is shown in an intermediateelevation and again a significant portion of the heat exchanger 201 isin a predominantly vertical convective air flow. In FIG. 4C, theconcentrating solar collector attached to cooling apparatus 103 is shownin a vertical elevation and a significant portion of the heat exchanger201 is once again in a predominantly vertical convective air flow.

FIGS. 4A-C also illustrate how the position of the photovoltaic cell(which is covered by the concentrating solar collector and thus notvisible in this depiction) is in all cases located below or at the samelevel as the heat sink regions of the heat pipe, i.e., the sourceregions of the heat pipe (areas where heat enters the heat pipe) arelower than the sink regions of the heat pipe (areas where heat exits theheat pipe). By so configuring the cooling system, good performance ofboth heat exchanger 201 and the vapor chamber 204 is achievable in allelevation angles. The dashed arrows in FIGS. 4A-C are adjacent to theregion of the cooling system experiencing substantially vertical airflow and indicate the direction of this convective airflow.

According to an exemplary embodiment, the term “substantially verticalorientation,” refers to a deviation from a perfectly vertical positionof no more than 45 degrees (with a deviation of 90 degrees beingconsidered a perfectly horizontal orientation). Thus, to illustrate thisprinciple, FIGS. 5A-C (which correspond to the exemplary orientations ofthe cooling apparatus 103 in FIGS. 4A-C, respectively) show how at leastone portion of the cooling apparatus is always in a substantiallyvertical orientation. For instance, in FIG. 5A (which corresponds to theorientation shown in FIG. 4A), a first portion of the cooling apparatus103 is in a perfectly vertical position.

In FIG. 5B (which corresponds to the orientation shown in FIG. 4B), botha first portion of the cooling apparatus 103 and a second portion of thecooling apparatus 103 are in a substantially vertical position since thefirst and second portions of the cooling apparatus deviate from aperfectly vertical position by less than 45 degrees, i.e., θ1 is lessthan 45 degrees and θ2 is less than 45 degrees.

In FIG. 5C (which corresponds to the orientation shown in FIG. 4C), asecond portion of the cooling apparatus 103 is in a substantiallyvertical position since the second portion of the cooling apparatusdeviates from a perfectly vertical position by less than 45 degrees,i.e., θ3 is less than 45 degrees. In the example shown in FIG. 5C, thefirst portion of the cooling apparatus is in a perfectly horizontalconfiguration.

FIG. 6 is a diagram illustrating an exemplary two-axis drive systembeing used in conjunction with a photovoltaic system, such as thephotovoltaic system of FIG. 1 that includes a concentrating solarcollector with a high power cooling apparatus attached thereto. As shownin FIG. 6, the photovoltaic system is mounted to a pedestal. Thepedestal can be rotated along a first axis, as indicated by arrows 602.The photovoltaic system is mounted to the pedestal by way of a pivot 604that permits the photovoltaic system to rotate along a second axis, asindicated by arrows 606. Thus, using this mounting configuration, thephotovoltaic system can be pointed in two dimensions to follow movementof the sun. By way of example only, rotating the photovoltaic systemalong the first axis (see arrows 602) allows for setting the azimuthangle (i.e., the position of the sun in the sky relative to a referencevector), and rotating the photovoltaic system along the second axis (seearrows 606) allows for setting the elevation. The concepts of azimuthand elevation would be apparent to one of skill in the art and thus arenot described further herein. Additionally, it is to be understood thatthe two-axis system drive system shown in FIG. 6 is merely exemplary,and any other suitable two-axis system that permits both azimuth andelevation adjustments may be similarly employed.

According to an exemplary embodiment, the two-axis drive system shown inFIG. 6 is equipped with motorized actuators (not shown) to permitautomated (e.g., remote, computer-controlled) adjustment of the azimuthand elevation positioning. The process for implementing such motorizedactuators in accordance with the present teachings would be apparent toone of ordinary skill in the art and thus is not described furtherherein.

FIG. 7 is a diagram illustrating an enlarged view 702 of a portion ofthe present plate fin heat exchanger (such as heat exchanger 201 of FIG.2) that highlights the plate and fins attached thereto as well as anoptional wrapper 704 that caps the fins. As shown in FIG. 7, the wrapperis configured to be open at the top and bottom of each fin so as topermit the formation of a convective airflow along the channelcontaining the fins. This open end wrapper configuration enhances theflow of air past the fins and improves the cooling capacity of thesystem in areas where wind is not usually present. According to anexemplary embodiment, the wrapper is made of a metal or plasticmaterial, such as aluminum, steel, acrylic, or other suitable sheetmaterial that can be bent or formed around the fins as shown and affixedto the assembly. The function of the wrapper is similar to a chimney inthat the buoyancy of air in the more vertical portions of the heatexchanger pulls the air through the more horizontal portions of the heatexchanger. Thus the purpose of the wrapper is simply to constrain theair flow along the length of the fins.

Although illustrative embodiments of the present invention have beendescribed herein, it is to be understood that the invention is notlimited to those precise embodiments, and that various other changes andmodifications may be made by one skilled in the art without departingfrom the scope of the invention.

What is claimed is:
 1. An apparatus for cooling a photovoltaic cell,comprising: a heat exchanger comprising a metal plate with a bendtherein that positions a first surface of the metal plate at an angle ofabout 100 degrees to about 150 degrees relative to a second surface ofthe metal plate, and a plurality of fins attached to a side of the metalplate opposite the first surface and the second surface, wherein each ofthe plurality of fins extends along an entire length of the side andcrosses the bend; a vapor chamber extending along the first surface andthe second surface of the metal plate, crossing the bend, such thatduring operation when the photovoltaic cell is attached to either thefirst surface or the second surface of the metal plate the vapor chamberis positioned to transport heat away from the photovoltaic cell, whereinthe vapor chamber is at least partially embedded in the metal plate; acladding material between the vapor chamber and the heat exchanger,wherein the cladding material is configured to thermally couple thevapor chamber to the heat exchanger; and a thermal spreader plate ateither the first surface or the second surface of the metal plate,wherein the thermal spreader plate is attached to, and in directphysical contact with, the vapor chamber, and wherein during operationthe photovoltaic cell is positioned on the thermal spreader plate overthe vapor chamber in a manner so as to be electrically isolated from themetal plate by the cladding material.
 2. The apparatus of claim 1,wherein the bend positions the first surface of the metal plate at anangle of about 140 degrees relative to the second surface of the metalplate.
 3. The apparatus of claim 1, wherein the heat exchanger is anaturally convective heat exchanger.
 4. The apparatus of claim 1,wherein the cladding material is configured to electrically isolate thevapor chamber from the heat exchanger.
 5. The apparatus of claim 1,wherein the cladding material comprises one or more of plastic, ceramicand glass.
 6. The apparatus of claim 1, wherein the vapor chambercomprises a heat pipe.
 7. The apparatus of claim 1, further comprising awrapper around the fins that is open at a top and a bottom to allowairflow along the fins, wherein the wrapper is formed of a metal orplastic material that is formed around the fins and affixed to the heatexchanger.
 8. A photovoltaic system, comprising: a cooling apparatus,comprising: a heat exchanger comprising a metal plate with a bendtherein that positions a first surface of the metal plate at an angle ofabout 100 degrees to about 150 degrees relative to a second surface ofthe metal plate, and a plurality of fins attached to a side of the metalplate opposite the first surface and the second surface, wherein each ofthe plurality of fins extends along an entire length of the side andcrosses the bend; a vapor chamber extending along the first surface andthe second surface of the metal plate, crossing the bend, wherein thevapor chamber is at least partially embedded in the metal plate; acladding material between the vapor chamber and the heat exchanger,wherein the cladding material is configured to thermally couple thevapor chamber to the heat exchanger; a thermal spreader plate at eitherthe first surface or the second surface of the metal plate, wherein thethermal spreader plate is attached to, and in direct physical contactwith, the vapor chamber; at least one photovoltaic cell thermallycoupled to the vapor chamber, wherein the photovoltaic cell ispositioned on the thermal spreader plate over the vapor chamber in amanner so as to be electrically isolated from the metal plate by thecladding material; and a concentrating solar collector attached toeither the first surface or the second surface of the metal plate andsurrounding the photovoltaic cell.
 9. The photovoltaic system of claim8, further comprising: a thermal interface material between the thermalspreader plate and the photovoltaic cell.
 10. The photovoltaic system ofclaim 9, wherein the thermal interface material comprises one or more ofa solder, a liquid metal thermal interface, a liquid metal alloy,thermal grease, a conductive particle filled organic thermal paste, aconductive particle filled organic thermal gel, a particle impregnatedpolymer and a phase change material.
 11. The photovoltaic system ofclaim 8, wherein the cladding material is configured to electricallyisolate the vapor chamber from the heat exchanger.
 12. The photovoltaicsystem of claim 8, wherein the bend positions the first surface of themetal plate at an angle of about 140 degrees relative to the secondsurface of the metal plate.
 13. A method for operating a photovoltaicsystem, comprising the steps of: providing the photovoltaic systemcomprising: a cooling apparatus having a heat exchanger comprising ametal plate with a bend therein that positions a first surface of themetal plate at an angle of from about 100 degrees to about 150 degreesrelative to a second surface of the metal plate, and a plurality of finsattached to a side of the metal plate opposite the first surface and thesecond surface, wherein each of the plurality of fins extends along anentire length of the side and crosses the bend, a vapor chamberextending along the first surface and the second surface of the metalplate, crossing the bend, wherein the vapor chamber is at leastpartially embedded in the metal plate, a cladding material between thevapor chamber and the heat exchanger, wherein the cladding material isconfigured to thermally couple the vapor chamber to the heat exchanger,and a thermal spreader plate at either the first surface or the secondsurface of the metal plate, wherein the thermal spreader plate isattached to, and in direct physical contact with, the vapor chamber; atleast one photovoltaic cell thermally coupled to the vapor chamber,wherein the photovoltaic cell is positioned on the thermal spreaderplate over the vapor chamber in a manner so as to be electricallyisolated from the metal plate by the cladding material; a concentratingsolar collector attached to either the first surface or the secondsurface of the metal plate and surrounding the photovoltaic cell; androtating the photovoltaic system to place the photovoltaic cell at aplurality of positions relative to a light source.
 14. The method ofclaim 13, wherein the system further comprises: a thermal interfacematerial between the thermal spreader plate and the photovoltaic cell.